Do fish sleep?

Just about all fish will spend part of each day asleep. Depending on the fish, being asleep can mean different things, but most fish don't sleep the same way we do. For instance, some fish (like herring and tuna) will remain motionless in the water during the night. While other fish, like rockfish and grouper, don't actually appear to sleep at all, but instead rest against rocks, bracing themselves with their fins. Furthermore, some freshwater fish (like catfish) will swim up under a log or beneath a river bank for shelter during the day.

Fish will have periods of restful inactivity, but they are usually far more aware of their surroundings than humans are when we sleep.

Also keep in mind fish can't close their eyes when they sleep; due to the fact that they don't have eyelids.